For a mechanical seal, which is an example of sliding component, to maintain sealing property for a long period of time, it must satisfy the mutually exclusive conditions of “seal” and “lubricate.” Particularly in recent years, the demand for lower friction is increasing further in the area of environmental protection, etc., as a means to prevent the sealed fluid from leaking while reducing mechanical loss at the same time. One way to reduce friction is to generate dynamic pressure between the sealing faces by means of rotation to create the so-called fluid lubrication state where the surfaces slide against each other with a liquid film in between. In this case, however, positive pressure generates between the sealing faces and the fluid flows from the sealing faces from the part subject to the positive pressure. This is the so-called lateral leak that occurs with bearings and corresponds to the sealing leak.
As shown in FIG. 8, traditionally with a sliding component used for the so-called “inside type” mechanical seal, etc., where high-pressure fluid (sealed fluid) is present on the outer periphery side and low-pressure fluid (atmosphere) on the inner periphery side of the seal area to seal the high-pressure fluid on the outer periphery side, multiple dynamic-pressure generation grooves 51a, 51b as well as multiple concave/convex parts 52a, 52b constituted by multiple fine parallel grooves are formed on a sealing face 50 in order to provide stable sliding properties regardless of the rotating speed of the rotational axis, in such a constitution that the dynamic-pressure generation groove 51a and concave/convex part 52a generate desired dynamic pressure and improve lubrication performance, respectively, when the flow direction of sealed fluid corresponds to the direction of arrow a, while the dynamic-pressure generation groove 51b and concave/convex part 52b generate desired dynamic pressure and improve lubrication performance, respectively, when the flow direction of sealed fluid corresponds to the direction of arrow b (hereinafter referred to as “Prior Art 1”; refer to Patent Literature 1, for example).
Also among the same so-called “inside type” mechanical seals, a mechanical seal is known, as shown in FIG. 9, where multiple fluid-introduction grooves 62 extending inward in a radial direction are formed on a seal area 61 of a rotating seal ring 60 in such a way that their outer end opens on the outward side in a radial direction while the inner end is present on the seal area, while dynamic-pressure generation grooves 63 continuing to these fluid-introduction grooves 62 and extending to one direction in the circumferential direction are formed, and as the rotating seal ring 60 is rotated in the direction of arrow a, fluid on the high-pressure fluid side (sealed fluid side) flows into the dynamic-pressure generation grooves 63 from the fluid-introduction grooves 62 to generate dynamic pressure between the seal area 61 of the rotating seal ring 60 and seal area of the stationary seal ring (hereinafter referred to as “Prior Art 2”; refer to FIG. 5 of Patent Literature 2, for example).
Also among the same so-called “inside type” mechanical seals, a mechanical seal is known, as shown in FIG. 10, where multiple wide spiral grooves 72 are formed on a seal contacting area 71 of a rotating seal ring 70 and narrow parts 73 extending to a position corresponding to 70 to 90% of the width of the seal contacting area 71 are provided on the tip side of the spiral grooves 72, with the spiral grooves 72 and narrow parts 73 set to different depths, respectively, in order to keep the seal contacting area in a non-contacting state by supplementing the static pressure effect when the dynamic pressure effect is small such as in a low-rpm condition, while keeping the seal contacting area in a non-contacting state via the dynamic pressure effect while turning even when the seal contacting area generates a strain that makes the end face higher on the outer side (hereinafter referred to as “Prior Art 3”; refer to FIGS. 4 to 6 of Patent Literature 3, for example).
However, Prior Art 1 presents a problem in that, regardless of the rotating direction, the dynamic-pressure generation grooves and concave/convex parts constituted by fine grooves are arranged in pairs in order to generate dynamic pressure and improve lubrication performance, and therefore cavitation always occurs at the negative step (step from the higher surface to the lower surface) between each pair of grooves during operation, which means that when this prior art is used as a mechanical seal for automotive water pumps, the constituents of sealed fluid may deposit onto, attach to, and accumulate on the sealing face due to cavitation, potentially leading to massive leakage.
On the other hand, Prior Art 2 presents a problem in that, although the depositing of the constituents of sealed fluid onto the sealing face due to cavitation is assumed to decrease, the fact that the dynamic-pressure generation grooves 63 do not directly continue to the high-pressure fluid side (sealed fluid side) means that, should any deposit be produced in the dynamic-pressure generation grooves 63 or any deposit or other foreign matter enter the dynamic-pressure generation grooves 63, such foreign matter is not discharged from, but remains inside, the dynamic-pressure generation grooves 63 to cause leakage.
Meanwhile, Prior Art 3 is intended to keep the seal contacting area in a non-contacting state by supplementing the static pressure effect when the dynamic pressure effect is small such as in a low-rpm condition, while keeping the seal contacting area in a non-contacting state via the dynamic pressure effect while turning even when the seal contacting area generates a strain that makes the end face higher on the outer side, which practically means that the high-pressure fluid entering the narrow parts 73 is used to obtain the static pressure effect in a low-rpm condition where the dynamic pressure effect is small, while the pumping action of spiral grooves 72 is used to generate dynamic pressure while turning, and no technical idea is disclosed to prevent cavitation.